In an electric resistance welded pipe forming mill for forming a pipe from a strip-shaped steel plate, a universal mill for forming strip material into various sectional shapes and so on, forming rolls in respective forming roll stands must be exchanged at high frequency, according to types and sizes of products. Therefore, for the purpose of easily exchanging the rolls in a short time, various devices and methods for executing the exchange have been heretofore proposed.
In case of exchanging only an inner roll unit in cage forming, the relevant inner roll unit is lifted by pulling it from an upper part of the roll stand. Thereafter, the inner roll unit is withdrawn in a direction of a width of material which is perpendicular to a product proceeding direction to be exchanged with a new inner roll unit which has been separately prepared, and the inner roll unit after the exchange is returned to the roll stand in a reverse flow to the above (PTL 1). In case of exchanging an upper roll unit in a pipe welding roll stand, it is also possible to conduct the exchange in the same manner (PTL 2).
In case of a four-way roll stand such as an electric resistance welded pipe forming mill and a mill, as a structure where an inner stand provided with four-way rolls is disposed in a post of the roll stand so as to move up and down, a method of exchanging an entirety of the inner stand with a new inner stand provided with the four-way rolls which has been separately prepared has been put into practical use (PTL 3).
However, in this structure, only the four-way rolls are mounted on the inner stand, and pressing devices such as jacks and various actuators to be connected thereto must be provided on an outer stand. Therefore, connection and disconnection between these devices are complicated, and additionally, works for mounting and detaching the rolls in the inner stand in an offline are also complicated. Moreover, it is necessary to prepare a plurality of the inner stands, and a large investment is required for storing these inner stands and for keeping a place for storage.
Accordingly, there has been proposed such a structure that an upper roll chock for pivotally supporting upper rolls, right and left side roll yokes for pivotally supporting right and left side rolls, and a lower roll chock for pivotally supporting lower rolls are assembled by stacking them in series by mutual insertion or pin connection thereby to form a stack body of the roll chocks, and the stack body is withdrawn in a horizontal direction perpendicular to a product proceeding direction to be exchanged with another stack body of the roll chocks which has been separately prepared (PTLs 4 and 5).